The TI99/4 was introduced in 1979 and was followed by the TI99/4a in 1981. The TI99/4 has upper case only, while the TI99/4a has both upper and lower case. (TI99 mail list). In 1983 the TI99/4a sold for $100 (Consumer Reports, p.475).
Processor: The TI99 series uses TI's TMS9900 microprocessor, which is capable of addressing 64k of RAM.
RAM: The TI99 came with 16k of video memory as well as only 256 bytes of main memory. The video memory was used by TI BASIC for storage.
Keyboard: The TI99 uses only a 48 key keyboard which uses a function key to obtain some characters such as quotes and the question mark, as well as arrow keys for cursor movement. As the TI99/4 does not have upper case, the shift key serves as the function key. On the TI99/4a there is a dedicated function key for this purpose. The TI99 keyboard contains all ASCII characters although some control characters can not be typed because they require the combination of the control and shift or control and function which is not recognized by the TI (TI99 mail list).
Video: The TI uses a composite video system, capable of 40x24 text resolution. The TI99/4 is unable to display lower case characters, while the TI99/4a has both lower and upper case. (TI99 mail list).
Storage: The TI99 has a cassette jack that allows connection of one or two standard cassette recorders. One cassette recorder can both save and play back stored information, while the other can only save data. TI also offered a floppy system that uses industry standard drives, so any low density disk drive can be used. TI's floppy controller is single density only but double density controllers were offered by other companies. TI has their operating system stored in ROM on the controller board. This ROM is limited to 40 tracks so if an 80 track drive is used half will go unused. Other companies offered controllers which contain ROMs that are able to use either 40 tracks or 80. (TI99 mail list).