IBM PC Emulator

An IBM PC Emulator written in C using SDL3

Building
Fonts
ROMS
Usage
- Command line
  - Definitions
- Configuration file
  - Definitions
XEBEC Hard disk drive
Sources
Screenshots

Emulated Hardware

i8086 CPU
i8237 DMA
i8253 PIT
i8255 PPI
i8259 PIC
i8272 FDC (NEC uPD765)
IBM Fixed Disk Drive (XEBEC)

Emulated ISA Cards

MDA ISA Card (IBM Monochrome Display Adapter)
CGA ISA Card (IBM Color Graphics Adapter)
FDC ISA Card
XEBEC ISA Card

Building

The project is built in Visual Studio 2022 or 2026

Dependencies	Github
I8086	https://github.com/tommojphillips/i8086
TOMI	https://github.com/tommojphillips/TOMI
SDL3 3.2.24	https://github.com/libsdl-org/SDL
SDL3_ttf-3.2.2	https://github.com/libsdl-org/SDL_ttf
ImGui 1.92.3	https://github.com/ocornut/imgui/tree/v1.92.3

Clone the repo and submodules

git clone --recurse-submodules https://github.com/tommojphillips/ibm_pc.git

cd dir to ibm_pc

cd ibm_pc

Fetch SDL3/SDL3_TTF VC Release

scripts\fetch_sdl3.sh

Open lib\UI\vc\UI.sln, build
Open vc\ibm_pc.sln, build, run.

Make sure these files are next to ibm_pc.exe or on your PATH:

SDL3.dll
SDL3_ttf.dll
UI.dll (built via UI.sln)

If building from source, and launching through visual studio, all .dll files are already on your PATH. You only need to copy the .FON files to the same directory as ibm_pc.exe

FONT Files

Font files are required for full functionality. FONTS can be found here: https://int10h.org/oldschool-pc-fonts/download/

Description	File
MDA Font 9x14	Bm437_IBM_MDA.FON
CGA Font 8x8	Bm437_IBM_CGA.FON

They have been included in the fonts\ directory of the repo.

ROM Files

ROMS are required for full functionality.

ROMS

Launching

Make sure these files are next to ibm_pc.exe:

Bm437_IBM_CGA.FON
Bm437_IBM_MDA.FON

Command-Line:

Switch	Switch (ALT)	Description	Values
`-config <config_file>`	`-c <config_file>`	Set the config file	file path
`-o <offset>`	N/A	Set the memory offset for the next ROM file.	`0x00000` - `0xFFFFF`
`<rom_file>`	N/A	Path to a ROM file. It is loaded at the current offset.	file path
`<A-D>: <disk_path>`	N/A	Load a disk image into a drive.	`A`, `B`, `C`, `D` ; file path
`-disk-write-protect`	`-dwp`	Write protect the next loaded disk.	N/A
`-disks <0-4>`	`-ds <0-4>`	Number of floppy drives present. 0-4.	`0` - `4`
`-video <video_adapter>`	`-v <video_adapter>`	Selects which display adapter to emulate	`MDA`, `CGA`
`-ram <ram>`	`-r <ram>`	Amount of conventional RAM.	16KB - 736KB
`-sw1 <sw1>`	N/A	Value of motherboard DIP switch SW1	`0` - `255`
`-sw2 <sw2>`	N/A	Value of motherboard DIP switch SW2	`0` - `255`
`-model <model>`	N/A	Motherboard model	`5150_16_64`, `5150_64_256`, `5160`
`-dbg`	N/A	Enables the debug UI	N/A

Notes

Numbers can be written in decimal, hexadecimal (0x), or binary (0b) form.
RAM can be provided in KB or BYTES.
When a ROM is loaded, -o is automatically incremented by the files size; You can chain ROM files with a single -o <offset>
If a DIP switch (sw1, sw2) isnt provided; it is set automatically based on the provided config

Example:

ibm_pc.exe -o 0xF6000 cb10_1.bin cb10_2.bin cb10_3.bin cb10_4.bin bios.bin -video CGA -ram 640 -model 5150_64_256 A: msdos4_startup.img

Means:
 Load cb10_1.bin (2K file) at 0xF6000
 Load cb10_2.bin (2K file) at 0xF8000
 Load cb10_3.bin (2K file) at 0xFA000
 Load cb10_4.bin (2K file) at 0xFC000
 Load bios.bin   (8K file) at 0xFE000
 Video adapter is a CGA Card
 640KB conventional RAM installed
 Model 64KB-256KB Motherboard
 msdos4_startup.img disk is in drive A:

Configuration File:

The emulator supports configuration files written in a custom structured INI-like format called TOMI

Settings:

Key	Type	Description	Values
`model`	ENUM	Motherboard model	`5150_16_64`, `5150_64_256`, `5160`
`video_adapter`	ENUM	Selects which display adapter to emulate	`MDA`, `CGA`, `CGA40`, `CGA80`
`conventional_ram`	INT	Amount of conventional RAM installed	`16K` - `736K`
`num_floppies`	INT	Number of floppy drives present	`0` - `4`
`sw1`	INT	Value of motherboard DIP switch SW1	`0` - `255`
`sw2`	INT	Value of motherboard DIP switch SW2	`0` - `255`
`sw1_override`	BOOL	Forces manual SW1 value instead of auto-calculated	`true`, `false`
`sw2_override`	BOOL	Forces manual SW2 value instead of auto-calculated	`true`, `false`
`disk`	STRUCT	Defines one or more floppy disk drives	See below
`hdd`	STRUCT	Defines one or more Hard disk images	See below
`rom`	STRUCT	Defines one or more ROM images	See below
`texture_scale_mode`	ENUM	Texture sampling mode	`Nearest`, `Linear`
`display_scale_mode`	ENUM	Display scaling behavior	`Fit`, `Stretched`
`display_view_mode`	ENUM	Display framing mode	`Cropped`, `Full`
`correct_aspect_ratio`	BOOL	Enables 4:3 aspect correction	`true`, `false`
`emulate_max_scanline`	BOOL		`true`, `false`
`allow_display_disable`	BOOL	Allow software to disable the display	`true`, `false`
`delay_display_disable`	BOOL	Delay the display disable (prevents flickering due to software disabling and enabling the display rapidly)	`true`, `false`
`delay_display_disable_time`	INT	The display disable delay time	milliseconds
`mda_font`	STRING	Path to the MDA font file	file path
`cga_font`	STRING	Path to the CGA font file	file path
`dbg_ui`	BOOL	Enables the debug UI	`true`, `false`

ROM settings:

Key	Type	Description	Values
`path`	STRING	Path to the ROM file	file path
`offset`	INT	The offset to load the ROM file	`0x00000` - `0xFFFFF`

DISK settings:

Key	Type	Description	Values
`path`	STRING	Path to the Disk file	file path
`drive`	INT	The drive to load the disk file in.	`A`, `B`
`write_protect`	BOOL	write protects the drive	`true`, `false`

HDD settings:

Key	Type	Description	Values
`path`	STRING	Path to the Disk file	file path
`drive`	INT	The drive to load the disk file in.	`C`, `D`
`geometry`	STRUCT	Geometry override for RAW images	See below
`type`	ENUM	Type override for RAW images	`Type1`, `Type2`, `Type13`, `Type16`

If loading a raw hard disk image; some geometries have ambiguous file sizes and cant determine the geometry from the file size alone.
Use geometry OR type parameter of the hard disk to tell the emulator what the disk geometry is.
If both geometry and type are supplied then the geometry is used to determine it.

GEOMETRY settings:

Key	Type	Description
`c`	INT	Max cylinders of the hard disk
`h`	INT	Max heads of the hard disk
`s`	INT	Max sectors of the hard disk

Type settings

See Hard disk drive geometries

Notes

Each disk, hdd or rom struct can appear multiple times to define multiple drives or ROMS.
Numbers can be written in decimal, hexadecimal (0x), or binary (0b) form.
Comments start with ; and extend to the end of the line.
Missing values fall back to defaults defined in the emulator.
If a sw1_override or sw2_override is false; the associated SW is set automatically based on the provided config
RAM must be provided in BYTES.

XEBEC

2 Image formats are currently support for hard disks. VHD or RAW/IMG images.

VHD

If using a VHD the geometry of the disk will be automatically detected since the VHD Stores the disk geometry. Using the VHD format allows you to browse a FAT12/FAT16 formated Hard disk in your Host OS like any other VHD.

A VHD cannot be saved while it is mounted in the Host OS.
A VHD can be loaded while it is mounted in the Host OS.
DOS will not see changes to the VHD made by the Host OS until a reboot of the emulator has been done. DOS caches the FAT and accessed files in RAM. Any new files created or modified might not show up until a reboot of the emulator. Using a program i have created i have been able to get around this issue. See FDFLUSH.COM

RAW IMAGE

If using a RAW image, Some hard disk geometries cant be determined from the file size alone due to multiple hard disk geometries having the same total size.

Hard Disk Geometries

Type	Geometry	Total size (MB)
`Type1`	C = 306, H = 4, S = 17	10.16MB
`Type2`	C = 615, H = 4, S = 17	20.41MB
`Type13`	C = 306, H = 8, S = 17	20.32MB (ambiguous)
`Type16`	C = 612, H = 4, S = 17	20.32MB (ambiguous)

Creating your Hard disk

[TODO]

Formating your Hard disk

Using FDISK/FORMAT

Load the unformatted hard disk in the emulator. For this demo; the hard disk is in Drive C:
Boot a DOS floppy in drive A: that has the FDISK and FORMAT utilities
Run FDISK to create a partition table on the hard disk.
Run FORMAT C: /s to format the hard disk and copy the system files to it.
Eject the floppy from drive A:
Reboot the emulator.

FDFLUSH.COM

This program invalidates the FAT and forces all floppies and hdds to be re-cached next time they are accessed. This allows changes made by the host OS to show up without a reboot of the emulator. This program can be found in the programs\ directory of the repo.

Sources

Sources.md

Name		Name	Last commit message	Last commit date
Latest commit History 130 Commits
config		config
fonts		fonts
images		images
lib		lib
programs/fdflush		programs/fdflush
scripts		scripts
src		src
vc		vc
.gitattributes		.gitattributes
.gitignore		.gitignore
.gitmodules		.gitmodules
Multiple Interrupts.txt		Multiple Interrupts.txt
config_file_format.md		config_file_format.md
ports.md		ports.md
readme.md		readme.md
roms.md		roms.md
sources.md		sources.md

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Repository files navigation

IBM PC Emulator

Emulated Hardware

Emulated ISA Cards

Building

FONT Files

ROM Files

Launching

Command-Line:

Notes

Example:

Configuration File:

Settings:

ROM settings:

DISK settings:

HDD settings:

GEOMETRY settings:

Type settings

Notes

XEBEC

VHD

RAW IMAGE

Hard Disk Geometries

Creating your Hard disk

Formating your Hard disk

Using FDISK/FORMAT

FDFLUSH.COM

Sources

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IBM PC Emulator

Emulated Hardware

Emulated ISA Cards

Building

FONT Files

ROM Files

Launching

Command-Line:

Notes

Example:

Configuration File:

Settings:

ROM settings:

DISK settings:

HDD settings:

GEOMETRY settings:

Type settings

Notes

XEBEC

VHD

RAW IMAGE

Hard Disk Geometries

Creating your Hard disk

Formating your Hard disk

Using FDISK/FORMAT

FDFLUSH.COM

Sources

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