A long running joke about Traveller has been the size of computers for starships, usually measured in displacement tons as being unrealistic. I find it to be acceptable because of what the machines are doing, the actual size of shipboard and mainframe computers, and general requirements. Also, traditionally, space opera has had large computers. A bit of background, I was assigned to a Ohio-class submarine, in Travller terms, a TL7 design with extensive TL8 electronics, and specialized in working with the computer system for the strategic weapon system.
A Model 1 computer takes up one displacement ton of the ship's volume. Considering a DTon is defined as exactly 13.5 Cubic Meters, that can be hard to visualized for those of us who don't deal with volumes every day. I found this from a moving company on how big their 15 cubic meter trucks are. Moving boxes are a good substitute here. Fan Lore in Traveller has been the Model 1 computer is roughly equivalent to a Cray-1 from the 1970's. Sized up, one of those units was 263 cm across the base, and 196 cm tall, taking up a volume of 10,647,740 cubic centimeters, or 10.64774 cubic meters. Throw in a bit of space for an operator, access and some ready spares, and 1 Dton is a nice round figure for design purposes.
As a strategic weapons system tech, I worked in a space just like the one at left. The brown doors in the background house various FCS components, and are integrated into a large scale forced air cooling system. Most of the doors contain power supplies to Versa Module Eurobus racks. Others have older, bulkier systems that have not been phased out, or high frequency AC power rectified into DC. Each one of those islands is about a Dton and a half of space. The beveled edges on the overhead into the islands are fan plenums, for cooling, and the deck is raised for an air return. Not pictured are the flat-panel displays for system control. I have said there is a minimum size for control units based on sophont physiology and ergonomics, so I don't see those getting much smaller. Also, there are various other computers running sonar and fire control, navigation, and communications.