I just got a 5150 and it came with hard drive installed

[mark66j]

It has a 65 watt power supply which I think is the stock version, and is not supposed to support a hard drive. I'm wondering if this was just someone's bad idea to try to make it work anyway, or whether this was done more often than I thought.

The motherboard has 5 slots and the cassette port, so it isn't an XT with a PC cover.

I probably will move this drive into an XT that I'm also getting, but I'm just curious about the setup of the 5150.

 

[mbbrutman]

IBM thought the power supply was too small to support a fully populated machine and the MFM hard drives of the time, so the XT was designed with a larger power supply. That doesn't mean it is bad or wrong to have a hard drive in a 5150 - just that at the time IBM didn't think so.

Keep in mind:

• The original XT hard drives were full height and had a fairly large power draw. If you have one of the smaller drives of the day (ST-225 for example), it would not be as taxing.
• IBM generally over engineered everything. The ratings on the power supplies were very conservative.
• Peak power consumption from a drive is at spin-up. Once it is spinning it doesn't draw as much power.

The only way to know if you are within specifications is to take some measurements.


Mike

 

[Dave Farquhar]

I've seen three 5150s that ended up with hard drives. My high school had a benefactor who worked for IBM. He enjoyed picking up old machines, fixing them up a little, and sending them in. He gave the school three 5150s with hard drives. I don't remember the specs on the drives anymore, only that they were big enough to hold DOS, MS Works, and Turbo Pascal, which was all we cared about. This was 1992, so they were really badly dated by then, but considering the school had PCs that didn't have hard drives at all, it could have been a lot worse. I used those three 5150s in my independent study my senior year.

 

[mark66j]

Thanks all for the info. When I bought this machine from eBay there was very little info on the machine's setup, and the only picture had a cover blocking the floppy and hard drive, so I was prepared for it to be missing both of them. The lever on the floppy (which is an original IBM full-height drive) is not working unfortunately -- it seems to be missing a hinge pin or something, so it won't close the top portion of the drive. But since the component on this are so huge compared to modern units, I think I can probably fix it (I've found my fingers are too fat to handle a lot of modern electronics repair).

 

[southbird]

Yeah the only time I ever had a 5150 PSU trip was when I tried to power a full height, 7 or so platter drive. It couldn't handle the initial draw very well.

 

[fragment]

yeah! i like this thread we need information from professionals on 5150's pc on how to get a mfm hard disk work there ... psu its a problem ... what we can do?

 

[modem7]

It's only the model A PCs that may have problems. The reason is that those came with 63W "Black" Powersupplies, and they were never meant to have hard drives. The model B PCs came with 130W PSUs, and could thus handle HDDs just fine.

All models of the 5150 were supplied with 63W PSUs (initially black, then silver). The 135W PSU was introduced in the 5160 (XT).

 

[Chuck(G)]

Absolute wattage ratings on PSUs can be misleading.

Most of the draw for a hard disk is on the +12 line which is used only by the floppy motors and some small current-draw sources, such as the 16K DRAMs on the 64K motherboard and the serial adapter.

The 63.5W PSU is nominally rated at 2A on the +12 line. A hard drive may have a startup surge current slightly greater than this without tripping the PSU overload circuit. As long as the running current is low enough, there really is no problem.

Early 5.25" floppy drives could be a bit greedy with the +12 also, but their surge doesn't really come until after the hard disk is spun up.

So, yes, it can work--barely. I've seen other 63.5W 5150s with hard drives and they seemed to have no problem.

Interestingly, switch-mode PSUs tend to exhibit greatest efficiency when near their load limit.