The Model 4 has a faster Z80A 4 MHz CPU,[5] larger video display of 80 columns by 24 rows, bigger keyboard, and can be upgraded to 128KB of RAM.

"[7] Commenting on its unexpected longevity as a Radio Shack product and object of aftermarket support by third-party companies, in May 1987 80 Micro magazine remarked, "Even when it was introduced in 1983, the Model 4 was seen as a last gasp for the TRS-80 line.

When the Model 4 boots into TRSDOS 6, the video display switches into 80×24 mode and the entire 64KB address space is mapped as RAM.

[13] Montezuma Micro sold a version of CP/M 2.2 that was customized for the Model 4's hardware: banked RAM, reverse video and assignable codes for the function keys.

Montezuma sold a terminate-and-stay-resident program they called Monte's Window, which provides functionality similar to Borland Sidekick.

DoubleDuty first appeared in Radio Shack's 1985 Computer Catalog (RSC-12), the same year that IBM's Topview, Apple's Switcher, and Quarterdeck's DESQview first became available.

[22] BYTE in October 1983 noted the lack of native software, but praised the Model 4's backwards compatibility and TRSDOS 6's new features.

The magazine concluded that the Model 4 "provides a lot of flexible computing power ... Radio Shack has a guaranteed winner".

This change greatly reduced the chip count and allows the circuitry for the Floppy Disk Controller and the RS-232 serial port to be included on the CPU board, making this new Model 4 a single-board computer, unlike the original 26-1069.

80 Micro published an article describing a simple motherboard modification to enable the installation of two external floppy drives.

Although criticizing the computer's lack of advanced documentation or double-sided drives, InfoWorld concluded that the 4P "is an outstanding product at an excellent price".

It is a Gate Array desktop machine featuring dual TEC FB-503 disk drives[28] with a capacity of 360KB each (double density sectors, 40 track, double-sided).

It supplies simple applications including a word processor, filer, spreadsheet, calendar, and mail manager.

This change in marketing resulted from Tandy corporation's desire to enhance its stature in the marketplace, because it was perceived by some in the computer press that the old "Radio Shack" moniker connoted an image of inferior quality.

During 1987–1988 the retail stores removed the Model 4Ds from display but they were kept in the yearly computer catalog and were available by special order through 1991,[30] when they were closed out for $599.