What does scaling horizontally mean?

Related questions

1. What is scalable distributed?
2. What are scalability issues?
3. What are scalable applications?
4. What's a scalable business?
5. What is difference between scale up and scale out?
6. What is scalable pricing?
7. What is scalable business?
8. Does vertical scaling improve availability?
9. What is scaling up and scaling out?
10. What is scalable web applications?

Tags

1. #scaling
2. #whereas
3. #machine
4. #power
5. #adding
6. #vertical
7. #resources
8. #scale
9. #machines
10. #means
11. #existing
12. #horizontal