Cassette Storage
TMS9902 with additional MODEM circuitry.  Default to 300 BAUD, but would work fine at 1200 BAUD.

16-Bit TMS9995 running at 12MHz (3MHz Internal).
64KB using eight TMS4164 DRAMs and a TMS4500A DRAM Controller.  Optional 74LS612 Memory Mapper allowed RAM to be expanded to 1MB.

Video Display
24KB using three TMS2564 EPROMs.   
TMS9928/29 Video Display Processor with 16KB VRAM using eight TMS4116 DRAMs.  Could be replaced by the Maplin V9938 MSX Video Card which had 128KB VRAM.
Floppy Disk

TMS9909 Floppy Disk Controller with up to four disk drives.  Drives were generally 5.25" in any combination of 40/80 tracks, single/double sided and single/double density.  3.5" drives could be substituted when used in Standard Density mode. 

Track format was 16 sectors/track, with either 128 or 256 bytes/sector.  An 80T DSDD disk could hold 640KB.

The TMS9909 was only available for a very short time, so a replacement FDC board was designed based on the TMS2797.
RS232 Port
TMS9902 Asynchronous Communications Controller (ACC).

TMS9911 Direct Memory Access Controller.  Two DMA channels, one of which was used by the TMS9909 FDC.
Full QWERTY keyboard with separate Function keypad.  General Instrument AY-5-2376 Keyboard Encoder.
Tech Specs
Cortex Basic in 24K EPROM.  This was a version of TI Power Basic that was modified and enhanced for the Cortex hardware.  Also included in the package was Monitor, a powerful Assembler/Disassembler/Debugger.  Cortex Basic included a BOOT command that was used to load a disk-based Operating System.

CDOS (Cortex Disk Operating System) extended Cortex Basic and Monitor with a Disk Filing System.

MDEX (Marinchip Disc Executive) was a complete Operating System from Marinchip Systems that ran on their M9900.  A Cortex version was made available by Micro Processor Engineering, Southampton, UK.  Once loaded, it completely replaced Cortex Basic and provided a rich programming and development environment.  Several languages were available (QBASIC, SPL, Pascal, Forth, Assembler), along with a professional Word Processor.