The SDS-5 (or SDS-V) was a really popular system, used by many of the big names in the 80's.
It was 'module' based so you could start with 5 modules and expand it to 6 or 7 in total.
5 x original black hex trigger pads & drum sound module all as pictured.
It's had a lot of use on many studio sessions but it's all fully working and sounds great.
The rack unit is still in very good cosmetic condition.
Here's a link to the Simmons page
here's a Youtube demo